Tom, greeting-card writer and hopeless romantic, is caught completely off-guard when his girlfriend, Summer, suddenly dumps him. He reflects on their 500 days together to try to figure out where their love affair went sour, and in doing so, Tom rediscovers his true passions in life.

The story follows a married couple, apart for a night while the husband takes a business trip with a colleague to whom he's attracted. While he's resisting temptation, his wife encounters her past love.

An advice columnist, Andie Anderson, tries pushing the boundaries of what she can write about in her new piece about how to get a man to leave you in 10 days. Her editor, Lana, loves it, and Andie goes off to find a man she can use for the experiment. Enter executive Ben Berry, who is so confident in his romantic prowess that he thinks he can make any woman fall in love with him in 10 days. When Andie and Ben meet, their plans backfire.

Though Rachel is a successful attorney and a loyal, generous friend, she is still single. After one drink too many at her 30th-birthday celebration, Rachel unexpectedly falls into bed with her longtime crush, Dex -- who happens to be engaged to her best friend, Darcy. Ramifications of the liaison threaten to destroy the women's lifelong friendship, while Ethan, Rachel's confidant, harbors a potentially explosive secret of his own.